Method of making magnetic cores



Oct. 5, 19430 J. c. GRANFIELD 2,339,324

METHOD OF MAKING MAGNETIC corms Original Filed Jan. 28, 1941 Fig.2.

Inventor:

John C. Granfield,

Patented Oct. 5, 1943 METHOD OF MAKING MAGNETIC cones John C. Granfield,Pittsfleld, Masa, assignor to General Electric Company, a corporation ofNew York Original application January 28, 1941, Serial No.

376,304. Divided and this application November 25, 1941, Serial No.420,425

3 Claims.

This invention relates to improvements in laminated magnetic corestructures for electrical induction apparatus such as transformers andreactors, and to methods for making such improved core structures.

This application is a division of my copending application S. N.376,304, filed January 28, 1941.

In the usual construction for magnetic ccresj the laminations are cut orpunched from relatively large stock sheets which are produced by arolling process from bars or' billets of a suitable magnetic materialsuch as silicon steel or a magnetic nickel iron alloy. The rollingprocess produces a grain structure in the sheets which may extend in thedirection in which the sheets have been rolled. The path of leastmagnetic resistance of such material is generally in the direction thatthe sheets have been rolled, though in certain types of steel the mostfavorable magnetic direction, in so far as low flux losses areconcerned, is at some angle with respect to the rolling direction. Ithas been found that optimum results for magnetic cores are obtained ifthe laminations are so cut from the sheets of magnetic material that thecore flux path is parallel with the path of least magnetic resistancethereof.

One common form of a magnetic core consists of a stack of L-shapedpunchings but it is obvious that such shapes cannot be punched as asingle piece from standard stock in such a manner that the mostfavorable magnetic direction extends parallel with the flux path in bothparts of the punching. This is due to the fact that the grain extends inthe same direction throughout all parts of the stock sheet while'the twotion to provide a new and improved core in which the laminations are socut from the metal stock that when fitted together into a unit, thecore.

flux may flow in the most favorable magnetic direction of thelaminations substantially completely throughout the magnetic circuit.

It is a further object of the invention to provide a new and improvedmethod of making low loss magnetic cores from metal stock with no Iwaste of material.

Further objects and advantages of the inven- I tion will appear from thefollowing description taken in connection with the accompanying drawing,while the features of novelty will be pointed out with greaterparticularity in the appended claims.

parts of an L-shaped punching are at right angles to each other. Anothercommon form of core consists of rectangular laminations stacked at"right angles with respect to each other. While the most favorablemagnetic direction in this type of core may be made parallel with thedirectlon of the flux'path throughout the central por- In the drawing,Fig. 1 is a view in perspective of a magnetic core employing my improvedlaminations; Fig. 2 is a view illustrating my improved method by whichthe laminations for the core of Fig. 1 are produced; Fig. 3 is a planview of a portion of a magnetic core illustrating a further modificationof the core illustrated in Fig. 1; Fig. 4 is a view illustrating themanner in which the laminations for the core of Fig. 3 are producedaccording to my improved method; Fig. 5 is a plan view of a magneticcore illustrating a still further modification oi the core shown in Fig.1; and Fig. 6 is a view illustrating the .netic core is shown havinglegs made up of stacks of laminations ll and yokes made up of stacks oflaminations II. The adjacent stacks are angularly arranged with respectto each other and in'the case of the rectangular core as shown, thestacks 'are arranged at right angles. The ends of the stacks are cut atan angle which is less than degrees and substantially equal to one-halfof the angle between adjacent stacks whereby the stacks may be fittedtogether in an end to end relation. In other'words, the diagonally cutend of each stack is substantially covered by the similarly orcooperatively cut end of the adjacent stack. It is not essential thatthe ends of each lamination of each stack be cut nations when the coreis assembled butt together in a parallel relation to form what will betermed a mitered joint between laminations of each layer and, hence,between the adjacent ends of each pair of angularly arranged stacks.

In order that the reluctance of the magnetic circuit be held to'aminimum, the butt joints between the lamination stacks must be madetight, and preferably means be provided for maintaining the tightness ofthe joints throughout normal usage of the device. Clamping means may beused for holding the leg and yoke portions tightly against each otherbut such clamps, if solely relied upon for this purpose, would in allprobability need to be tightened to such an extent that internal strainsmay be produced thereby in the laminations which in turn would adverselyaffect the magnetic properties of the metal.

In the modification illustrated in Fig. 1, the ends of the laminationsare so shaped and fitted together that a tight joint is assured betweenthe leg and yoke stacks without requiring tight clamping means. Thelaminations II and 12 are each provided at one end with a dovetailprojection l3 extending perpendicularly from the diagonal edge and anopening or indentation N in the opposite end for cooperatively receivinga similar dovetail projection of the adjacent lami nation. Theprojections l3 and the cooperating openings l4 are so matched that whenthe laminations are fitted together in the assembly of the core, therewill be no appreciable gap between the ends of adjacent laminations. Itwill be obvious that after the core has been assembled, subsequentseparation of the legs and yokes of the core will be substantiallyprecluded by virtue of the interlocked portions.

In assembling the lamination layers it is preferred that adjacent layersbe oppositely arranged so that the projections at the ends of thelaminations of adjacent layers will extend in opposite directions. Withthe layers so arranged, edgewise shifting of the laminations of onelayer with respect to each other will be precluded. Only a relativelylight clamping means need be provided for holding the lamination layerstogather and such clamping means need notbe drawn so tight as to set upany appreciable strains in the metal of the laminations.

The laminations II and [2 are so cut from the stock sheets of metal thatthe most favorable magnetic direction of the metal will run lengthwiseof the laminations. When the laminations are assembled as illustrated.due to the mitered joints at the corners of the core, the core flux mayflow through the leg and yoke portions substantially continuously in themost favorable magnetic direction of the metal throughout the magneticcircuit and substantially without cutting crosswise of such direction atany point. A highly efllcient magnetic circuit is thus provided.

The laminations are formed from a strip of magnetic material in a mannerillustrated in Fig. 2. The strips of magnetic material such as siliconsteel or a magnetic nickel iron alloy are preferably produced by thehigh reduction cold rolled process from bars or billets so that thestrips have a granular structure, the grain extending longitudinally ofthe strips and parallel to their side edges and having the mostfavorable magnetic direction substantially parallel with the graindirection. The strips may be of any desired width and of indefinitelength. The strips are preferably of the exact width of the laminationsto be used in the magnetic core.

The laminations are cut or punched fro such a strip l5 by any suitablemeans (not shown) such as a suitable set of dies. The strip is cutcrosswise at recurrent intervals, depending upon the length of thelaminations to be formed, and at an angle substantially equal toone-half of the angle which is to be formed by two adjacent laminationstacks. The direction of the cut across the strip is alternated, or

in the case of laminations for a rectangular core when each cut will bealong a base line at 45 degrees to the strip edge, the alternate cutswill be displaced by degrees from the others. In order that theprojection provided on the diagonal end of one lamination will registeraccurately with the opening thus formed in the end of the next adjacentlamination when placed at right angles with respect thereto, theprojection should extend from the exact center of the diagonal and beexactly symmetrical on both sides of a perpendicular erected from thecenter of the diagonal. It will be obvious that the leg laminations Ilmay all be punched from one strip and the yoke laminations l2 fromanother, or they may be punched alternately from the same strip asillustrated in Fig. 2. By either method of punching the laminations,there will be no waste of material.

The particular configuration for the dovetail joints between the leg andyoke laminations is immaterial, it being important only that it be sodesigned that a minimum amount of metal extend into the flux path withthe grain thereof at an angle other than that of the core flux path.

In producing the cores by this method it is preferred to first punch outthe laminations in the manner described and then form desired shapessuch as L, U, or rectangular by interlocking component parts and thenannealing the assembled shape. By assembling the shapes first and thenannealing them with a proper heat treatment to remove strains producedin the metal by the punching operation, the interlocked parts willenlarge slightly to further tighten the joint and thereby practicallyeliminate the gap effect.

In certain types of cores, it may not be necessary to interlock thelaminations in order to insure a sumciently tight joint between thediagonally cut ends. The modifications of core structures illustrated inFigs. 3 to 6, inclusive, are particularly suitable for smaller sizedcores, or in cores built up from relatively thin laminations. Themagnetic core of Fig. 3 comprises stacks of laminations forming legs 20and yokes 2| the laminations for which are so punched from stock sheetsof magnetic material that the most favorable magnetic direction thereofextends substantially parallel with the flux path through thelaminations, as in the previously described modification. The oppositeends of the leg and yoke laminations are cut diagonally so that theright angularly arranged laminations of each layer fit together at thecorners with mitered joints as in the core described above. In thismodification, however, the diagonal edge at one end of each of thelaminations is provided with a non-interlocking projection 22 while theopposite diagonal edge is provided with a corresponding notch 23 forcooperativelyreceiving the projection of an adjacent right angularlyarranged lamination. As illustrated, the projection and the cooperatingnotch may be of a semi-circular configuration, although it is to beunderstood that the projection and notch may be of any other suitableshape.

In the assembly of the core of this modification, the laminations ofeach layer are fitted closely together so that there will be a minimumof space between adjacent ends. The adjacent lamination layers are alsooppositely arranged so that the projections of the adjacent laminationlayers will extend in opposite directions, as is indicated by the dottedlines in Fig. 3. With the laminations assembled in this manner theprojections of each lamination will overlap with portions of rightangularly extending laminations of adjacent layers on the opposite sidesthereof. The lamination layers may then be compressed by any suitableclamping means (not shown) which are so applied as not to set up anyappreciable internalstrains within the metal of the laminations whichmight adversely affect the magnetic properties thereof. Due to thefrictional resistance between the overlapping portions of the'adjacentlamination layers, separation of the leg and yoke portions of the coreat the joints will be substantially precluded.

While the laminations for the leg and yoke portionsof the core may beout from stock sheets of magnetic material of any dimension with themost favorable magnetic direction extending parallel to the path of thecore flux through the laminations, it is preferred that the laminationsbe punched from a relativelylong narrow strip or one having the samewidth as the laminations. as shown in Fig. 4. The manner of punching thelaminations from th strip is similar to that described above inconnection with Fig. 2. In order that the laminations will fit properlytogether when arranged at right angles with respect to each other, itwill be necessary that the diagonal edge be at an angl of 45 degreeswith respect to the side edges of the strip and that the projection andthe notch provided on the opposite diagonal edges of each lamination besymmetrical on the opposite sides of a perpendicular erected from thecenter of the diagonal. With the ends of the laminations so punched, itwill be obvious that the parts may be fitted accurately together with noappreciable gap between the adjacent end edges.

In Fig. 5' is illustrated a further modification of the invention inwhich a magnetic core is shown comprising leg portions and yoke portions3| which are also fitted together with generally diagonally miteredcorner joints but oi a slightly different configuration than thosepreviously described. In this modification one end of each of thelaminations is provided with a triangular projection 32 which extendsfrom a true diagonal line while the opposite end is provided with acorresponding notch 33 for cooperatively receiving a similar projectionfrom a lamination extending at right angles with respect thereto.

The base of the triangular projecting portion of each lamination, thatis, along the line of the diagonal, is preferably just slightly narrowerthan the length of the diagonal, while the height of the triangle is ofthe order of one-fourth of the width of the base. Thus, it will beobserved that the width of ach lamination increases progressively fromzero at the outermost end to maximum width at the inner corners of thediagonal edges. The rate of progressive increase of width varies fromminimum to maximum along the end edge of the laminations depending uponthe particular angle of the two sides of the triangular projection andrecess with respect to the side edges of the laminations. It will beevident, therefore, that the core flux will fiow lengthwise, or in themost favorable direction throughout the full length of each lamination,with a fairly uniform distribution of the core flux throughout the crosssection of the core.

As in the preceding modification, the adjacent layers of laminations areoppositely arranged as indicated by the dotted lines of Fig. 5 in orderthat the end portions of the laminations of adjacent layers will overlapeach other. When the core clamps are applied in a manner as describedabove, the frictional resistance between the overlapping portions of thelaminations of consecutive layers of the core will substantiallypreclude separation of the leg and yoke portions of the core throughsubsequent use of the device in which the core is incorporated.

In Fig. 6 is illustrated the manner in which the laminations for thecore of Fig. 5 are produced from a long strip 35 of magnetic materialwhich is similar to the strip I5 described above. Thus in cutting thestrip generally diagonally crosswise as described above to produce aplurality of lengths, adjacent cuts are provided with portions extendingin a generally diagonal direction substantially degrees with respect toeach other.

The assembled core described above with offset diagonally extending buttjoints at the corners which may be assembled from the laminationsproduced by the method claim herein is described and claimed in myabove-mentioned copending application. As in the previous modification,in order that the laminations will fit properly together with a tightjoint between the diagonal ends, the triangular projection from thediagonal should be symmetrical on the opposite sides of a perpendicularerected from the center of the diagonal.

While the invention has been described with particular reference tomagnetic cores for transformers and reactors, it is obvious that theinvention is applicable to magnetic cores generally, in-

cluding those for motors, generators and other rotating apparatus aswell as to other forms of stationary induction apparatus.

Having described the principle of my invention in what 1 consider torepresent certain preferred embodiments thereof, I desire to have itunderstood that the invention is not to be limited to the specific formsdescribed but that I intend in the appended claims to cover all suchmodifications as 3111 within the true spirit and scope of the inven-What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of making a low loss rectangular magnetic core from rolledstrip material having the most favorable magnetic directionlongitudinally of the strip which comprises forming laminations byrecurrently cutting across said strip along a broken lineformingprojections and corresponding interfitting indentations, the oppositeends of which are along a straight line at a 45- degree angle with oneedge of said strip, the intermediate portion of which broken line issymmetrical on opposite sides of a perpendicular erected from the centerof said straight line, then cutting across said strip along a similarbroken lineforming projections and corresponding interfittingindentations spaced from said first broken line and displaced 90 degreestherefrom, and assembling the laminations with projections oflaminations interfitting indentations of the adjacent laminations toform a layer for the magnetic core.

2. The method of making a low loss laminated rectangular magnetic corefrom rolled strip magnetic material having the most favorable magneticdirection extending longitudinally of the strip, said method comprisingcutting across said strip generally at a 45-degree angle in oppositedirections with respect to the magnetic direction of the strip at pacedintervals along a broken line forming projections and correspondingindentations symmetrical on opposite sides of a perpendicular erectedfrom the center of a 45-degree line, and assembling said laminationswith adjacent ends at right angles with respect to each other and withthe adjacent end edges of said 20 laminations abutting each other in aparallel relation.

3. The method of making a laminated magnetic core of high efiiciency andeconomy for an electromagnetic induction apparatus from rolled stripmaterial having substantially more favorable magnetic properties in thedirection of rolling, said method including the steps of cutting thestrip generally diagonally crosswise into a plurality of lengths with anindentation and a corresponding projection fitting and filling theindentation so as to produce a cut with substantially no scrap,providing the adjacent cuts with portions extending in a generallydiagonal direction substantially 90 degree with respect to each other,and assembling the cut lengths with a projection of a length fitting theindentation of an adjacent length to form a layer of laminations for themagnetic core. I

JOHN C. GRANFIELD.

